Prevailing torque nuts are (usually) a deformed version of a hexagonal nut, often with an integral flange washer, and the intention is for the binding and prevailing torque to take place between the threads of the nut and the bolt (screw, stud or other externally threaded element), as the nut is threaded onto the bolt. Normally, the nut is applied with a power wrench or other method, and the person carrying out this operation will preset the wrench to a specified value, in accordance with a tightening specification. If the assembly subsequently loosens, the nut will remain in place and will strongly resist being shaken loose through vibration because of the prevailing torque.
Although there are numeous methods available, many of which are patented, for applying a deformation to a hexagonal nut in order to deform it or at least a portion of it, so that binding will take place between the nut and the bolt on which it is threaded, to date a satisfactory degree of consistency of deformation has been lacking. This has meant that many of the produced nuts were rejects, as being either too greatly deformed or too little.